1. Field of the Invention
The present invention relates generally to the field of metal matrix composite materials including those materials which have high, cross-sectional Barn values including ceramics, and metals including but not limited to boron, samarium and gadolinium oxides, nitrides, carbides and silicides thereof. These ceramic's and metal additives are used for attenuating neutrons in nuclear fuel. The invention relates more specifically to an apparatus and method for producing such materials with high strength, high density and durability and large ingot sizes.
2. Background Art
Most methods for producing metal matrix composites use liquid mixing and dry powder Iso-pressing technology. Liquid mixing is very limited in regard to the size and type of particulates, which can be stirred or mixed into the molten melt. Harmful metal-ceramic reactions, which occur at elevated temperatures during the melt, limited percentages of ceramic particulate additive and low specific strength and stiffness are all problems associated with molten stir fabrication of metal matrix composites. Iso-pressed metal matrix composites show good specific strength and stiffness but have a problem with the ingot production size. This problem is associated with available Iso-press equipment. The maximum inner diameter of the largest manufactured high pressure Iso-press is approximately 12 inches. Because of consolidation shrinkage and latex bag tooling, the largest ingot diameter that could be produced is approximately 8 inches. Low green density areas are also evident in the center area of the Iso-pressed 8-inch metal matrix ingots. These present processing problems and reduce physical strength properties of the composite. Because of such size limitations, large cross-sectional extrusions cannot be made and high extrusion ratios, which are a key to producing good physical properties, cannot be accomplished.